1. Field of the Invention
The present invention relates in general to a flow molding process and associated apparatus. More particularly, the invention pertains to the forming of thermoplastic parts using radio-frequency heating. Even more particularly the invention is described herein, in connection with a radio-frequency dielectric heating process for forming a finished foam plastic piece.
2. Background Discussion
Reference is now made to the present inventor's prior U.S. patents. This includes U.S. Pat. No. 4,268,238 granted May 19, 1981 and pertaining to a flow molding apparatus that is particularly adapted for the construction of three-dimensional pieces. This patent describes a flow molding process and associated molding apparatus for making plastic parts or pieces utilizing a radio-frequency heating field along with means for applying constant pressure, along with an even temperature gradient, to the plastic part. The other prior art of the present inventor is U.S. Pat. No. 4,441,876 granted April 10, 1984 and also relating to a flow molding process and associated molding apparatus for making plastic parts or pieces utilizing a radio-frequency heating technique. This particular patent relies upon the matching of dielectric constants. The apparatus in this patent is in particular employed for forming pieces having different thicknesses throughout. The purpose being to provide uniform heating throughout the piece being fabricated regardless of the varying thicknesses thereof.
It is an object of the present invention to provide an improved method and associated apparatus for molding plastic pieces of the type formed from a foamable plastic compound.
Another object of the present invention is to provide an improved method and associated apparatus for molding plastic pieces which are particularly adapted for the fabrication of pieces having non-uniform thickness throughout.
A further object of the present invention is to provide a flow molding process and associated apparatus wherein the molds are of simple construction and wherein the process can be carried out without great complexity.
A further object of the present invention is to provide a flow molding technique employing a radio-frequency field for heating and in which the technique is adapted to provide uniformity of heating of the material as well as providing for a reduction in the time required for carrying out the heating and formation step.